The prior art is generally cognizant of window blinds utilizing vertical slats adapted to turn about their longitudinal axes. For typical examples see Woodle, U.S. Pat. No. 4,006,769; Galex, U.S. Pat. No. 3,921,694, and Takashi Niwa, U.S. Pat. No. 3,499,477. The vertically disposed slats may be made of a variety of materials, including rigid materials such as wood, plastic, or metal, and flexible materials such as fabrics. For an example of the latter, see Nestor, U.S. Pat. No. 2,828,816.
For esthetic reasons, among others, wooden slats are often preferred in window blinds. However, such slats are frequently subject to warping, being generally thin and long so that a great deal of surface is exposed to atmospheric changes. Furthermore, because of their considerable length, even slight warping per unit of length may have a significant cummulative effect, resulting in a visually objectionable distortion of the slats and also a disruption of their function, in that bowed slats fail to properly engage the edges of adjacent slats so as to screen out light or provide privacy. One response to the problem of warping is seen in McGlone, U.S. Pat. No. 2,275,975. In McGlone an effort is made to control the direction of the wood grain in the slats relative to the flat faces of the slats.